It sounds like there are questions out there that I may be able to help answer. I am going to start with the question about exercising and shoulder pain.
Obviously, shoulders were not made for the repetitive use and stress that they are put under when your arms are used for mobility. Shoulder pain is exacerbated by muscle imbalances - the primary motions/forces you are going through are pushing down. You push down to propel a wheelchair, you push down to transfer, you push down to do a pressure relief. All this use of the pecs cause them to get stronger and tighter. It brings your shoulder blades around the rib cage, giving a rounded shoulder look. This decreases the space on the front of the shoulder where all the rotator cuff tendons, peripheral nerves, and blood supply to the arms run. This can set up the rotator cuff tendons to rub on the acromion with overhead movement.
What can help? First of all - stretch those pecs!! In a doorway is good (I'm hoping the picture I attach shows up) as long as you are getting your shoulder blade back and down. You could also lay on your back and open your arms up - increased the stretch with a towel roll down your spine. You also want to stretch your biceps because they too get tight when that shoulder blade is stuck in a forward position. For the doorway stretch, just straighten out your arm and turn more. You should feel the stretch down the biceps if you're doing it right.
Stretch every day! Hold each for 20 seconds and do it 3 times.
Exercising is great, but you don't want to work out those muscles that are already overused and tight. You want to work out those muscles that are supposed to hold your shoulder blade back. When those pecs are tight, and the shoulder blades are curved, the muscles in the back are lengthened, and therefore weaker. Exercise them to get them stronger while stretching to get those shoulder blades to stay back where they are supposed to be.
A band is sufficient. Pullies are good too.
1. Rows - holding arms straight out, pull the elbows back
2. Shoulder external rotation - keep your elbow at your side, with a 90 degree angle, and pull the band/pulley away from your stomach
3. Shoulder adduction - with you arm straight out to the side (don't go above the shoulder) pull the band straight down. Keep the elbow straight.
4. This is a tricky one, if you hold your arms straight out in front of you, keeping the elbows straight, you want to push the arms forward so the shoulder blades come around the rib cage. Think of a boxer giving a hook and how the shoulder blade comes around to get a better reach.
I would recommend a light weight that does NOT increase your pain, and doing 2 sets of 15, 3 times a week. If you have shoulder pain, ice your shoulders after the exercises. I know - ice sucks! No one likes it. But it helps! Keep it on for 20 minutes.
Let me know if you have any questions. Hope that is a good start. Feel free to ask about anything you think a PT can help with.